In recent years, sleep apnea syndrome (SAS), wherein respiration cannot be performed during sleep, is known as a pathology related to respiration during sleep.
The diagnosis of sleep apnea syndrome is generally made by a doctor, etc., after an all-night polysomnography (PSG) test in, for example, a hospital has been conducted.
However, the PSG test is a large burden on a patient who takes the test, because it requires the patient to wear, for example, a band for measuring movement of the abdomen, on the abdomen, etc., and to sleep with a sensor for measuring nasal respiration inserted in the nose. Furthermore, a burden is also placed on the hospital where the PSG test is conducted.
Therefore, there have been conducted simple tests in which arterial blood oxygen saturation or nasal respiration is measured by, for example, a device (sensor) which can be easily attached to the patient, whereby a respiratory arrest state (apnea state) of the patient is estimated.
It should be noted that sleep apnea syndrome, described above, is mainly classified into obstructive SAS (OSAS), wherein an airway is obstructed and so respiration is arrested, and central SAS (CSAS), wherein a respiration command from the brain is not issued and so respiration is arrested. Obstructive SAS and central SAS differ in treatment, and thus need discrimination from each other.
However, in the above-described simple tests, obstructive SAS and central SAS cannot be discriminated from each other. It is therefore desired that even a simple test conducted by a device which can be easily attached to a patient provide information helpful in discriminating between obstructive SAS and central SAS (that is, information helpful in the diagnosis of sleep apnea syndrome).